Imine-based Ligand Research Articles

Assembly of four d10-metal inorganic–organic hybrid coordination polymers based on bipyrazine imine-based ligand: Synthesis, crystal structures and luminescent properties

Four new inorganic–organic hybrid coordination polymers {[Ag2L(NO3)2]·H2O}n (1), [Ag2L(SCN)2]n (2), [CdL(SCN)2]n (3), and [CdLI2]n (4) have been synthesized and structurally characterized by IR spectroscopy, thermogravimetric (TG) analyses and complete single crystal structure analyses, where L is 2,5-bis(pyrazinyl)-3,4-diaza-2,4-hexadiene. The structure of polymer 1 is a 3D coordination framework containing Ag-(μ-NO3−) inorganic bridging units, in which each L coordinates four silver atoms through two pyrazinylimine chelate units and two terminal monodentate pyrazinyl N donors. Polymer 2 displays a new 3D inorganic–organic hybrid network through the coordination interactions between Ag-(1,1,3-μ-SCN−) inorganic 2D sheets and bidentate bridging ligands with two terminal monodentate pyrazinyl N donors. Bidentate bridging ligands link 1D inorganic chains Cd-(1,3-μ-SCN−) system for 3 and Cd-(μ-I−) system for 4 to form a similar two-dimensional layer network. The luminescent properties of polymers 1–4 were investigated in the solid state at room temperature.

Synthesis, Crystal Structure, and Luminescent Properties of One Cadmium(II) Coordination Polymer with Mixed Imine-based Bidentate Schiff-Base and Thiocyanate Ligands

A new one-dimension Cd(II) coordination polymer [CdL2(NCS)2] n (L = (C5H4N)C(CH3) = N−N = C(CH3)(C5H4N)) has been synthesized and characterized by IR, UV, elemental analysis, TG technique and X-ray crystallography. Cd(II) atom has an distorted octahedral environment with a N6 donor set from four ligands and two NCS− anions, respectively. A pair of ligands bridge two adjacent Cd(II) centers to form one dimension chain structure containing bimetallic 22-membered macrometallacyclic rings. A 1D structure is held together with its neighboring ones via multiform hydrogen bonds to form a 3D supramolecular structure. The luminescent properties of the complex at room temperature were investigated.

Effect of bridging ligand structure on the thermal stability and DNA binding properties of iron(ii) triple helicates

Triple helical di-iron complexes, readily prepared through interaction of iron(II) ions with imine-based ligands, are cylinder-shaped tetracations comparable in size and shape to common protein DNA recognition units. They have a strong tendency to coil DNA, and have recently been found to induce formation of three-way junctions in palindromic oligonucleotides. To introduce potential H bond acceptor units onto the surface of triple-helicates, new iron(II) complexes have been synthesized in which the central linking unit in the bridging ligand is S or O, instead of CH(2). The DNA binding properties of these new metallo-helicates were studied using UV-vis spectroscopy and circular and linear dichroism. Results show that the three iron triple helicates bind the DNA in a similar way but that the stability of the triple helicate unit is decreased with the O linked bridging ligand.

Design, Synthesis, and Characterizations of a Series of Pt4 Macrocycles and Fluorescent Sensing of Fe3+/Cu2+/Ni2+ Through Metal Coordination

A Pt(II)(2) organometallic "clip" (1a) containing ethynyl functionality is synthesized. Multinuclear NMR and electrospray ionization mass spectrometry characterized this "clip", and the molecular structure was determined in an X-ray single-crystal diffraction study. A series of discrete molecular rectangles (2a-d) have been synthesized from this "clip" in combination with dipyridyl-based linear linkers (L(1-4)) by a metal-ligand coordination driven self-assembly approach [where L(1) = 4,4'-bipyridine, L(2) = trans-1,2-bis(4-pyridyl)ethylene, L(3) = N-(4-pyridyl)isonicotinamide, and L(4) = N,N'-bis(4-pyridylidene)ethylenediamine]. Rectangle 2d was designed using the imine-based ligand L(4) to make it a system composed of a fluorophore-receptor-fluorophore combination. The imine N(4) pocket is the receptor site, while the anthracene-based "clip" is the fluorophore. Complex 2d is fluorescent in nature and showed fluorescence quenching in solution upon the binding of hard transition metal ions (Fe(3+), Cu(2+), Ni(2+), and Mn(2+)) into the N(4) pocket. The nonresponsive nature of the fluorescence intensity upon the addition of soft metal ions (Zn(2+) and Cd(2+)) having d(10) configuration makes it a suitable sensor for transition metal ions. The fluorescence intensity of the Ni(2+) bound complex was regained when the metal was removed by a stronger chelating 2,2'-dipyridyl ligand.

Crystal structures of metal–organic frameworks sustained by π–π interactions between triple-helices

Metal–organic frameworks [(Fe2L3)·(C4H10O)] 1, [(Fe2L3)·(C5H5N)] (2), [(Fe2L3)·(C6H6)] (3) and [(Fe2L3)·(C4H8O)4] (4), achieved from triple metal helical iron complex Fe2L3, were assembled in the solvents of diethyl ether/DMF, pyridine, benzene and THF, respectively, where H2L is one of the simplest imine-based ligands {[(C6H4)(OH)]CHN–NCH[(OH)(C6H4)]}. Compounds 1, 2, 3 and 4 all crystallize in a centro-symmetric space group, consequently the molecules occur as a racemic mixture of Δ–Δ and Λ–Λ configuration enantiomers, wherein the equivalent fragments are related by the C2 axis. The phenyl rings of the helical units contact the neighbors via π–π (face-to-face) and C–H⋯π interactions to form two-dimensional channeled frameworks in which solvent molecules are absorbed in the channels in each of the structures. Thermogravimetric analyses reveal that the solvent molecules can be evacuated from the pores without loss of the framework periodicity. The crystal lattice is thermally stable up to 350 °C, and diethyl ether can be re-adsorbed by putting the heated material in diethyl ether solvent. It is also interesting to find that upon addition of other solvents such as n-hexane and cyclohexane, thermal gravimetric measurement and elemental microanalysis do not support the absorbance of these guests, indicating that the inclusion can be selectively re-absorbed. All the results indicate that although C–H⋯π interactions have energies that are only in the range of 2–20 kJ mol−1, these interactions are significant enough in combination that the orientation of molecules in the solid can be predicted with a reasonable degree of accuracy.

Synthesis and crystal structure of a triangular nickel(ii) complex with the shortest imine-based rigid ligand

A novel triangular complex [Ni(SCN)2L]3 was generated via self-assembly from Ni(SCN)2 and the readily prepared imine-based ligand L, (C5H4N)–CHN–NCH–(C5H4N), by appropriately adjusting the coordination conditions of the metal center.

Self-assembly of tetrahedral M4L6 clusters from a new rigid ligand

Self-assembled tetrahedral [M4L6]8+ (M = Zn2+, Cu2+) clusters were generated from a simply prepared conjugate imine-based ligand with two bidentate binding sites separated by a biphenyl group.